These days a lot of mobile devices communicate with each other using Internet Protocols (IP). To provide such mobile devices with mobility support, IETF (Internet Engineering Task Force) proposes a client-based mobility management protocol known as mobile IP (Mobility Support in IPv6, hereinafter called MIP) as indicated in the following Non-Patent Document 1 and a network-based mobility management protocol known as a proxy mobile IP (PMIP) as indicated in the following Non-Patent Document 2.
According to the MIP, each mobile node has a permanent home network. When the mobile node attaches to the home network, a primary global address known as a home address (HoA) is assigned to the mobile node. When the mobile node moves outside the home network and attaches to another foreign network, a temporary global address known as a care-of address (CoA) is assigned to the mobile node. According to the concept of the mobility support, even when the mobile node attaches to a foreign network, a packet addressed to the HoA is reachable for the mobile node. This reachability is implemented by providing an entity known as a home agent (HA) in the home network. The mobile node registers its own CoA with the HA using a message known as a binding update (BU) message. This registration allows the HA to create binding between the HoA and the CoA of the mobile node. Then, the HA intercepts a message addressed to the HoA of the mobile node and transfers the packet to the CoA of the mobile node using packet encapsulation. This packet encapsulation sets the packet addressed to the HoA of the mobile node in a new packet payload, and is also known as packet tunneling.
This MIP copes with problems for mobility, but has several problems. One of these problems is that the mobile node itself needs to transmit a BU message to its own HA. This means that a mobile node moving at high speed has to generate a large number of BU messages. A mobile node at a geographically remote place from its own HA may take more time to transmit a BU message to the HA. When the HA starts transferring of a packet addressed to an updated CoA, the mobile node may be no longer located at such a transfer destination. For these reasons, network-based local mobility management is proposed as disclosed in IETF RFC 5213 (Non-Patent Document 2) and the following Patent Document 11 and Patent Document 9. In this method, a mobile node can use the same address continuously even when the mobile node changes a point of attachment in a local network domain, and therefore the frequency to transmit a BU message to the HA of the mobile node can be reduced.
The network-based local mobility management (Net LMM) uses one local mobility anchor (LMA), a plurality of mobile access gateways (MAGs) and one AAA (Authentication Authorization and Accounting) server. The MAG operates as an access router as well for a mobile node attaching the MAG. Every time a mobile node attaches to the MAG, the MAG firstly verifies a credential of the mobile node with the AAA server so as to authorize the mobile node for qualification to use services in the local network domain. The AAA server further informs the MAG of a prefix, i.e., an address to be assigned to the mobile node. This procedure allows the MAG to advertise the same prefix known as a home network prefix (HNP) to the mobile node. At the same time the MAG needs to update the LMA so as to tunnel a packet transmitted to the prefix assigned to the mobile node to a MAG the mobile node currently attaches to. This update is implemented by transmitting, from the MAG to the LMA, a proxy BU (PBU) message binding the address the mobile node uses with the MAG address.
This procedure is known as proxy mobile IP (PMIP) as well, because the MAG as a proxy of the mobile node transmits the PBU message to the LMA, and the LMA operates as a home agent of the mobile node in the local network domain. In this way, irrespective of which MAG the mobile node attaches to currently, the mobile node always refers to the same home network prefix (HNP), and therefore does not change its own address. As a result, there is no need for the mobile node to frequently transmit a BU message to its own home agent.
Meanwhile, various wireless techniques have been rapidly introduced, for instance, increased number of mobile nodes are available equipped with various access interfaces such as UMTS cellular interface, wireless Ethernet® 802.11 interface, WiMAX® (802.16) interface and Bluetooth® interface. In order to support a device provided with a plurality of interfaces in the local mobility management, a plurality of prefixes, i.e., addresses are assigned to the device. According to IETF RFC 5213 in Non-Patent Document 2, a mobile node refers to a different prefix for each of a plurality of interfaces, and this prefix is maintained as long as the mobile node roams in the same network. When the mobile node is a MIP node roaming in a foreign domain, such a mobile node needs to configure a plurality of CoAs (one CoA from each prefix) and bind the plurality of CoAs with its own HoA. This is because, when the mobile node wants to use all interfaces communicated with the home agent (HA) and the correspondent node (CN), the mobile node needs to transmit a plurality of BU messages to the HA and the CN using mechanisms described in the following Non-Patent Document 3 “IETF Draft Multiple CoA” and the following Non-Patent Document 4 “IETF Draft Flow Binding”.
Currently, network-based mobility management in a pure sense is not available. Cellular-based systems can use mechanisms such as SIP (Session Initiation Protocol) protocol and a protocol disclosed in the following Patent Document 7. However, in order to redirect a typical IP session over different interfaces, tunneling techniques as disclosed in the following Patent Documents 1, 2, 3 and 5 may have to be used. This is because, during redirecting, an original packet having a prefix assigned to a first interface as a destination is routed to a second prefix as a different prefix. Further, when a prefix as a destination is different, a router on the route may execute Ingress filtering to discard the packet.
The tunneling techniques may require an IP tunnel or a layer-2 bearer terminated at the mobile node, and therefore the processing load and the packet size will increase. As one method to avoid the tunneling techniques, a router along the path may be informed so as to let a packet addressed to a prefix pass even when the prefix is not the one assigned to a target interface. This method, however, cannot be used for the case where the router on the route is a legacy (not knowing a prefix P1 of a first connection), and the router is not easily changed at low cost. As another method, as disclosed in the following Patent Document 8, an anchor point may change a packet address. This method may allow a mobility anchor to change a destination address of a packet to a second address within a range of a prefix assigned to a target interface to which the packet is to be routed. This method can avoid Ingress filtering by the router on the route without the need of any special encapsulation.